Vapor compression types of refrigeration systems are employed in a wide range of applications, such as, cooling building interiors, and in freezer and refrigerator units in a wide range of sizes and different configurations. Typically, such systems employ a compressor to increase the temperature and pressure of a gaseous refrigerant. The output of the compressor then is supplied to a condensor, where the gaseous refrigerant is changed to a liquid refrigerant. Liquid refrigerant from the condensor is supplied through an expansion valve into an evaporator which is used to absorb heat energy from the surrounding air or other medium to be cooled. Gaseous refrigerant leaving the evaporator then is supplied back to the compressor, where the cycle is repeated.
It has been found in such systems that the liquid refrigerant leaving the condensor frequently includes bubbles of gaseous refrigerant in it. This tends to reduce the efficiency of the system. Thus, a greater amount of refrigerant must be used at a higher pressure than otherwise would be the case if a complete conversion from gas to liquid took place in the condensor prior to supplying the refrigerant to the expansion device or expansion valve at the evaporator.
Currently there is much concern also over the effects of escaped refrigerant upon the ozone layer surrounding the earth. Scientific studies indicate that the ozone layer is being destroyed by chemicals of the type used in refrigeration systems throughout the world. As increased amounts of such refrigerants are released into the atmosphere, through leaks or in other ways, serious and possibly permanent damage to the ozone layer is taking place. Consequently, it is desirable, to the extent possible, to minimize the amount of refrigerant required in any given system for accomplishing the desired cooling purpose. The amount of refrigerant used in any given cooling system is referred to as the "charge" of that system.
Obviously, if the amount of refrigerant can be reduced without a corresponding reduction in the cooling capacity of the system, several advantages occur. First of all, there is less refrigerant available to leak into the atmosphere to cause damage to the ozone layer. In addition, the cost of the refrigerant for the system is reduced since less refrigerant is used. Finally, when less refrigerant is required in a given system, the pressure of the refrigerant provided by the compressor does not need to be as high as when a greater amount of refrigerant is present. This results in a reduction of the mechanical strain on the sytem, thereby increasing the useful life of the various components used in the refrigeration system.
Efforts have been made in the past to improve the efficiency of refrigeration systems by inserting a sub-cooler in the system between the output of the condensor and the input to the expansion device for the evaporator. Sub-coolers for accomplishing this purpose are disclosed in the two patents to Lavigne U.S. Pat. Nos. 4,142,381 and 4,207,749. In the systems disclosed in these patents, the refrigerant leaving the condensor is sprayed into the interior of a sealed heat exchanger. The heat exchanger operates as a sub-cooler and has a cooling medium circulated through cooling coils located in it. The cooling medium is provided from an external source, such as a cool water supply or the like. The refrigerant sprayed into the interior of this heat exchanger comes into contact with the cooling coils and is reduced in temperature. The liquid refrigerant collecting at the bottom of the heat exchanger then is supplied to the expansion valve for the evaporator.
The system of these patents however, has a disadvantage because of the necessity to provide a separate coolant for the sub-cooler heat exchangers from a source outside of the refrigeration system itself. Four other patents disclosing systems which do not require an external coolant for a refrigeration sub-cooler, but which use a tapped off portion of the refrigerant to cool the main refrigerant in a sub-cooler unit, are the U.S. Pat. Nos. to Manning 4,316,366 and 4,357,805; Woods 4,696,168 and Nunn 4,577,468. All of these patents disclose systems in which a sub-cooler chamber is utilized between the condensor and the expansion valve for the evaporator. A heat exchange unit is provided through which the main refrigerant passes. A portion of the main refrigerant is tapped off and supplied through an expansion valve to a cooling coil or a cooling jacket to provide sub-cooling to the main refrigerant passing through the unit. The diverted vaporized refrigerant which is used to provide this sub-cooling is supplied back to the suction line from the evaporator to join the vaporized refrigerant from the evaporator prior to resupplying the refrigerant to the compressor for the system.
The systems of these four patents all provide some degree of sub-cooling to the main refrigerant. These systems, however, do not function to eliminate any entrained gas bubbles in the liquid refrigerant, since the refrigerant line essentially is the same as in conventional systems, except that it does pass through the sub-cooler unit. In addition, a single heat exchange chamber or a single cooling coil is employed in these systems, so only a limited amount of sub-cooling can be accomplished in them.
A different approach for a refrigeration sub-cooler is disclosed in the U.S. Pat. Nos. to Osborne 3,553,974; Adams 4,694,662; and Barron 4,683,726. In the systems of these patents, the output of the condensor is supplied through a sub-cooler chamber in which the entire amount of coolant from the condensor is sprayed through a spray bar into the interior of the sub-cooler. This causes a flashing of some of the coolant; and, theoretically, the refrigerant is cooled as a result of the slight pressure reduction and flashing which takes place in the sub-cooler chamber. In addition, the bubbles of gaseous refrigerant theoretically are removed, so that only liquid refrigerant is withdrawn from the sub-cooler at the bottom.
In the system of the Osborne Patent, the gaseous vapor which is present in the sub-cooler chamber is withdrawn from the top and supplied back to the suction line at the input of the compressor. The Barron Patent recognizes a drawback of the overall systems disclosed in Osborne and Adams, and places the sub-cooler in the cold air stream passing out of the evaporator to supplement and enhance the sub-cooling function of the sub-cooler. As disclosed in the Barron Patent, it is necessary to place a sub-cooler of the type disclosed in Osborne and Adams in a cool air stream or another cooling heat exchange environment in order effectively to provide any sub-cooling action.
It is desirable to provide a refrigeration sub-cooler which overcomes the disadvantages of the prior art sub-coolers mentioned above, which is efficient and effective in operation, which does not require a separate cooling medium, and which both sub-cools the liquid refrigerant and removes gaseous bubbles from it during operation.